Optical fiber base material manufacturing apparatus

ABSTRACT

An optical fiber base material manufacturing apparatus including a reaction chamber; a burner that has a portion thereof inserted into the reaction chamber through an insertion opening that creates a connection between the inside and outside of the reaction chamber, and emits a flame toward a starting member positioned within the reaction chamber; and a seal connection member that creates an air-tight seal between the burner and the reaction chamber at the insertion opening. One end of the seal connection member firmly contacts the burner inserted therethrough, another end of the seal connection member firmly contacts the reaction chamber and has a through-hole formed therein through which the burner is inserted without contacting the seal connection member, and the seal connection member includes a connecting portion that connects the one end to the other end, while preventing transfer of stress between the one end and the other end.

The contents of the following Japanese patent application areincorporated herein by reference:

-   -   NO. 2014-258193 filed on Dec. 22, 2014.

BACKGROUND

1. Technical Field

The present invention relates to a manufacturing apparatus for anoptical fiber base material.

2. Related Art

VAD (Vapor phase Axial Deposition) and OVD (Outside Vapor Deposition)are known as methods for manufacturing an optical fiber base material.With these methods, a silicon compound such as silicon tetrachloride(SiCl₄) is provided in an oxyhydrogen flame obtained by burning hydrogenand oxygen in a reaction chamber. A porous base material is grown bydepositing silicon dioxide (SiO₂) microparticles generated from thesilicon compound resulting from the hydrolytic reaction. The porous basematerial obtained in this manner is heated and sintered, therebyobtaining a transparent optical fiber base material, as shown in PatentDocument 1, for example.

-   Patent Document 1: Japanese Patent Application Publication No.    H1-239033

However, there are cases where changes occur in the quality of theporous base material during the process for growing the porous basematerial.

SUMMARY

According to a first aspect of the present invention, provided is anoptical fiber base material manufacturing apparatus comprising areaction chamber; a burner that has a portion thereof inserted into thereaction chamber through an insertion opening that creates a connectionbetween the inside and outside of the reaction chamber, and emits aflame toward a starting member positioned within the reaction chamber;and a seal connection member that creates an air-tight seal between theburner and the reaction chamber at the insertion opening. One end of theseal connection member firmly contacts the burner inserted therethrough,another end of the seal connection member firmly contacts the reactionchamber and has a through-hole formed therein through which the burneris inserted without contacting the seal connection member, and the sealconnection member includes a connecting portion that connects the oneend to the other end, while preventing transfer of stress between theone end and the other end.

According to a second aspect of the present invention, provided is Anoptical fiber base material manufacturing method comprising using anoptical fiber base material manufacturing apparatus that includes areaction chamber; a burner that has a portion thereof inserted into thereaction chamber through an insertion opening that creates a connectionbetween the inside and outside of the reaction chamber; and a sealconnection member that creates an air-tight seal between the burner andthe reaction chamber at the insertion opening. One end of the sealconnection member firmly contacts the burner inserted therethrough,another end of the seal connection member firmly contacts the reactionchamber and has a through-hole formed therein through which the burneris inserted without contacting the seal connection member, the sealconnection member includes a connecting portion that connects the oneend to the other end, while preventing transfer of stress between theone end and the other end, and the method comprises emitting a flamefrom the burner toward a starting member positioned inside themanufacturing apparatus.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a manufacturing apparatus 10 formanufacturing an optical fiber base material 210 using VAD.

FIG. 2 is a schematic view of a seal structure between the reactionchamber 110 and the burner 130.

FIG. 3 is a schematic view of the burner boot 140.

FIG. 4 is a graph showing the refractive index distribution in theradial direction of an optical fiber base material 210.

FIG. 5 is a schematic view of a seal structure between the reactionchamber 110 and the burner 130.

FIG. 6 is a graph showing the refractive index distribution in theradial direction of an optical fiber base material 210.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, some embodiments of the present invention will bedescribed. The embodiments do not limit the invention according to theclaims, and all the combinations of the features described in theembodiments are not necessarily essential to means provided by aspectsof the invention.

FIG. 1 is a schematic view of a manufacturing apparatus 10 formanufacturing an optical fiber base material 210 using VAD. Themanufacturing apparatus 10 includes a reaction chamber 110, a raisingmechanism 120, a burner 130, a video camera 150, a console 160, and aPID controller 170.

The reaction chamber 110 surrounds a starting member 220 and an opticalfiber base material 210 that is formed at the tip of the starting member220, and isolates the optical fiber base material 210 and the startingmember 220 from the outside atmosphere. The starting member 220 at thetime when the manufacturing of the optical fiber base material 210begins and the optical fiber base material 210 that has been attached tothe starting member 220 are output from the top end of the reactionchamber 110 in the drawing. Therefore, the reaction chamber 110 mayinclude a lid or the like that opens and closes. The reaction chamber110 includes an insertion opening on a side surface into which theburner 130 is inserted, and this insertion opening is described furtherbelow with reference to FIG. 2.

The raising mechanism 120 has the starting member 220 hanging therefrominside the reaction chamber 110, via a dummy rod 230, and raises thestarting member 220 and the optical fiber base material 210 attached tothe starting member 220 upward in the drawing while rotating the opticalfiber base material 210 and the starting member 220 on the axis of thestarting member 220.

The burner 130 emits a flame onto a region near the bottom end of thestarting member 220 hanging within the reaction chamber 110 or onto aregion near the bottom end of the optical fiber base material 210attached to the starting member 220. The burner 130 is a multi-pipeburner made of quartz glass, for example, and the flow rate of theburner 130 can be controlled by a mass flow controller, for example. Theburner 130 supplies hydrogen gas and oxygen gas for generating theoxyhydrogen flame, as well as a raw material gas such as SiCl₄ servingas a raw material and GeCl₄ serving as a dopant raw material, into thereaction chamber 110.

A plurality of burners 130 are arranged in the manufacturing apparatus10 shown in the drawing. The burner 130 that is arranged at the bottomposition in the drawing and deposits soot on the center portion emitsraw material gas including a Ge dopant onto the soot deposition bodybeing raised toward the top of the reaction chamber 110 in the drawing,and deposits glass microparticles that become the core having a highrefractive index.

A burner 130 that is arranged further upward in the drawing and depositssoot on the surface of the soot deposition body is supplied with rawmaterial gas that does not include the Ge dopant, and deposits glassmicroparticles with a low refractive index to form the cladding. In thisway, a plurality of burners 130 that each have different specificationsand supply gases with different compositions are provided.

The video camera 150 captures an image of the region near the bottom endof the optical fiber base material 210 in the drawing, which is theregion being grown within the reaction chamber 110. The image capturedby the video camera 150 is displayed in a display section 161 of theconsole 160.

The console 160 detects the raising speed of the optical fiber basematerial 210 caused by the raising mechanism 120 and calculates theaverage value of this raising speed, for example. The console 160compares the average value of the calculated raising speed to a presetraising speed, and calculates the difference therebetween. Furthermore,the console 160 corrects the flow rates of the gases supplied to theburners 130 according to the calculated difference. Yet further, theconsole 160 controls the raising speed of the optical fiber basematerial 210 resulting from the raising mechanism 120 via the PIDcontroller 170.

When manufacturing the optical fiber base material 210 using VAD and themanufacturing apparatus 10 described above, in a state where theposition and orientation of the burners relative to the reaction chamber110 are fixed, the flames generated by the burners 130 are emittedtoward the starting member 220. As a result, the SiO₂ microparticlesdoped with Ge and the SiO₂ microparticles that do not contain Gegenerated by the hydrolytic reaction in the oxyhydrogen flames generatedby the burners 130 are sequentially deposited to form the optical fiberbase material 210.

The deposition floor surface 211 is monitored by the manufacturingapparatus 10 via the video camera 150 and the display section 161, andthe raising speed resulting from the raising mechanism 120 is controlledsuch that the position of the deposition floor surface 211 of theoptical fiber base material 210 relative to the burners 130 ismaintained at a prescribed height. Furthermore, the average movementover time of the raising speed controlled in the manner described aboveis monitored, and the flow rate of the gas supplied to the burners 130is adjusted based on this value, in order to stabilize the raisingspeed. As a result, the refractive index distribution of themanufactured optical fiber base material 210 is made more consistent inthe longitudinal direction of the optical fiber base material 210. Inthis way, the elongated optical fiber base material 210 is manufacturedwith a desired stable refractive index distribution across the lengththereof.

When forming the optical fiber base material 210, hydrogen chloridegenerated from the raw material gas and SiO₂ microparticles that are notdeposited on the optical fiber base material 210 are produced. Therelease of these materials to the outside atmosphere is undesirable.Therefore, an exhaust pipe connecting to the inside of the reactionchamber 110 is provided, and the exhaust gas including the hydrogenchloride gas, the SiO₂ microparticles, and the like may be sent to anexternal treatment facility.

FIG. 2 is a schematic view showing the sealing structure between thereaction chamber 110 and the burners 130. Components that are the sameas those shown in FIG. 1 are given the same reference numerals, andredundant descriptions are omitted. With the manufacturing apparatus 10shown in the drawing, an air-tight seal is formed by the burner boot 140between the reaction chamber 110 and the burner 130.

With the manufacturing apparatus 10 shown in the drawing, a protrudingportion 111 is provided as the insertion opening for a burner 130 in thereaction chamber 110. The protruding portion 111 is shaped as a shortcylinder passing into the inside of the reaction chamber 110. Theprotruding portion 111 has a flange portion 112 that expands to theradial outside of the protruding portion 111 formed at the tip thereof,along a surface that intersects the direction in which the protrudingportion 111 protrudes. Furthermore, the inner diameter of the protrudingportion 111 is larger than the outer diameter of the burner 130 insertedtherethrough. Accordingly, the reaction chamber 110 including theprotruding portion 111 does not directly contact the burner 130.

With the manufacturing apparatus 10 shown in the drawing, the burnerboot 140 is an example of a sealing connection component, and is formedby silicon rubber that is white and translucent. The burner boot 140includes a hollow connecting portion 143 and a flange portion 142 andend portion 144 at each end of the connecting portion 143. Each flangeportion 142 and end portion 144 is open, and it is possible to insert aburner 130 connected to an end portion of a gas supply line 131 into theburner boot 140.

The flange portion 142 of the burner boot 140 is secured relative to theflange portion 112 of the protruding portion 111 of the reaction chamber110, by a boot pressing jig 141. The flange portion 142 on the burnerboot 140 side and the flange portion 112 on the reaction chamber 110side have substantially the same shape and are firmly attached to eachother. As a result, an air-tight connection is established between thereaction chamber 110 and the burner boot 140

The inner diameter of the end portion 144 of the burner boot 140 isslightly less than the outer diameter of the burner 130 inserted intothe end portion 144. Therefore, the end portion 144 of the burner boot140 elastically deforms to stretch as a result of the burner 130 beinginserted. Accordingly, the end portion 144 of the burner boot 140automatically forms a tight connection with the outer surface of theburner 130, as a result of the elastic force of the burner boot 140itself.

The connecting portion 143 of the burner boot 140 is generallydome-shaped, and has an inner diameter that is substantially equal tothe inner diameter of the protruding portion 111 of the reaction chamber110 on the side where the flange portion 142 is provided. On the sidewhere the flange portion 142 is provided, the burner boot 140 does notcontact the burner 130 inserted therein.

The connecting portion 143 of the burner boot 140 has a curved shape atthe end surface that includes the central axis of the burner 130.Therefore, when the relative positions of the flange portion 142 sideand the end portion 144 side of the burner boot 140 are changed, theconnecting portion 143 deforms easily and the transfer of stress betweenthe flange portion 142 and the end portion 144 is cut off. As a result,with the manufacturing apparatus 10, the displacement or deformation ofthe reaction chamber 110 caused by change in temperature, for example,is prevented from being communicated to the burner via the burner boot140.

The gas supply line 131 that supplies the raw material gas and the liketo the burner 130 may be formed by a flexible material. As a result,when making fine adjustments to the position at which the burner 130 issecured, rigidity of the gas supply line 131 is prevented from becomingan impediment.

It should be noted that the resin material, elastomer, or the like thatis the preferred material for the flexible gas supply line 131 ispreferably not arranged inside of the reaction chamber 110, inconsideration of thermal resistance and oxidation resistance.Accordingly, the back end of the burner 130 extends to the outside ofthe reaction chamber 110, and the gas supply line 131 is preferablyconnected to the burner 130 outside of the reaction chamber 110.

(Manufactured Example)

FIG. 3 shows an exemplary burner boot 140 in the manufacturing apparatus10. Components of the burner boot 140 that are the same as those shownin FIG. 2 are given the same reference numerals, and redundantdescriptions are omitted. The burner boot 140 of the manufacturingapparatus 10 includes a flange portion 142, a connecting portion 143,and an end portion 144.

In the burner boot 140 that has a total length of 50 mm, the flangeportion 142 is positioned on the left side in the drawing, and is aportion that is shaped as a circular lid with a hole in the center. Theflange portion 142 has an outer diameter of 80 mm, which issubstantially the same as the outer diameter of the flange portion 112of the protruding portion 111 in the reaction chamber 110. The flangeportion 142 has an inner diameter of 50 mm, which is substantially thesame as the inner diameter of the protruding portion 111 on the reactionchamber 110 side.

The flange portion 142 of the burner boot 140 has a thickness of 4 mm.Therefore, when sandwiched together with the flange portion 112 of theprotruding portion 111 by the boot pressing jig 141, the flange portion142 elastically deforms to create an air-tight connection with theflange portion 112 on the reaction chamber 110 side. As a result, theend portion on the flange portion 142 side of the burner boot 140 formsan air-tight connection with the reaction chamber 110.

In the manufacturing apparatus 10, the outer diameter of the cylindricalburner 130 inserted into the burner boot 140 is 26 mm. Accordingly,there is a large gap between the burner 130 inserted into the burnerboot 140 and the inner surface of the hole of the flange portion 142,such that these components do not contact each other. Therefore, evenwhen the protruding portion 111 of the reaction chamber 110 and theflange portion 142 of the burner boot 140 are displaced due to thermalexpansion of the reaction chamber 110, for example, these components donot contact the side surface of the burner 130.

In the end portion 144 of the burner boot 140 positioned on the centerright side in the drawing, the inner diameter of the burner boot 140 is24 mm. As described above, the outer diameter of the burner 130 insertedinto the burner boot 140 is 26 mm. Accordingly, when the burner 130 isinserted into the end portion 144 of the burner boot 140, the burnerboot 140 elastically deforms by widening from the inside at the endportion 144. As a result of the elasticity of the burner boot 140 thatattempts to compensate for this elastic deformation, the end portion 144of the burner boot 140 forms air-tight contact around the burner 130,and this state is maintained.

At the end portion 144 of the burner boot 140 described above, the innerdiameter of the burner boot 140 may decrease while drawing closer to theend portion 144. In this way, the burner 130 can be inserted more easilyand the surface area of the portion where the burner 130 and the burnerboot 140 are in contact with each other is increased, thereby improvingthe air-tight seal.

In the burner boot 140, the flange portion 142 and the end portion 144described above are connected in an air-tight manner by the connectingportion 143. The connecting portion 143 has a total thickness of 1 mm.The connecting portion 143 has a curved cross-sectional shape in a crosssection obtained by cleaving along a plane that includes the centralaxis. Therefore, the connecting portion 143 is dome shaped, and is lessrigid than the flange portion 142. Accordingly, when the flange portion142 is displaced, the stress experienced by the burner boot 140 due tothe displacement is barely transferred to the end portion 144 on theopposite side. Furthermore, the displacement experienced on the endportion 144 side is barely transferred to the flange portion 142. Inother words, the connecting portion 143 blocks the transfer of stressbetween the flange portion 142 and the end portion 144.

As a result, the burner boot 140 is easily deformed by the connectingportion 143, and therefore, when adjusting the position of the burner130, particularly when making fine adjustments, the burner boot 140having one end secured to the reaction chamber 110 is prevented frominterfering with the displacement of the burner 130. Furthermore, whilethe optical fiber base material 210 is being manufactured, even if theprotruding portion 111 and the flange portion 112 are displaced due tothermal expansion of the reaction chamber 110, this displacement isabsorbed by the connecting portion 143 of the burner boot 140 and nottransferred to the burner 130. Accordingly, regardless of the state ofthe reaction chamber 110, the position of the burner 130 is stable andit is possible to perform deposition on and raise the optical fiber basematerial 210 while the angle of elevation or the like of the burner 130is kept in an initially set state, and to manufacture the optical fiberbase material with stable optical characteristics along the lengththereof.

Furthermore, even when the relative positions of the burner 130 and theprotruding portion 111 of the reaction chamber 110 are changed, theair-tight seal between the burner 130 and the reaction chamber 110 ismaintained by the burner boot 140, and the gas inside the reactionchamber 110 does not leak to the outside. Furthermore, impurities areprevented from entering into the reaction chamber 110 through theportion connecting the reaction chamber 110 and the burner 130.

Specifically, in the burner boot 140, the flange portion 142 connectedto the reaction chamber 110 and the end portion 144 connected to theburner 130 are distanced from each other. Furthermore, the thick flangeportion 142 of the burner boot 140 firmly contacts the flange portion112 of the protruding portion 111, and therefore, even when the burnerboot 140 is deformed, the air-tight seal of the flange portion 142 doesnot deteriorate. The end portion 144 of the burner boot 140 firmlycontacts the burner 130 as a result of the elasticity of the burner boot140, and therefore, even when the burner boot 140 is deformed, theair-tight seal of the flange portion 142 does not deteriorate. Inaddition, the connecting portion 143 of the burner boot 140 is soft, andtherefore the connecting portion 143 deforms in a manner to follow thedisplacement of the flange portion 142 and the end portion 144, therebymaintaining the air-tight seal without breaking.

It is obvious that the shape and dimensions of the burner boot 140 arenot limited to the example described above. The dimensions can bedetermined according to the specifications of the reaction chamber 110and the burner 130 being used. Furthermore, the shape of the burner boot140 at the flange portion 142 and the end portion 144 can be determinedaccording to the shape of the reaction chamber 110 and the burner 130used. The connecting portion 143 is not limited to having a dome shape,and can have a variety of shapes such as a stepped shape, a bellowsshape, a spindle shape, or the like.

The inner diameter of the burner boot 140 at the end portion 144 may begreater than or equal to 80% and less than 100% of the outer diameter ofthe burner 130 inserted therethrough. In this way, the air-tight sealbetween the burner 130 and the burner boot 140 at the end portion 144 isensured. If the inner diameter of the end portion 144 is less than 80%of the outer diameter of the burner 130, the fastening pressure causedby the end portion 144 is high and there are cases where a burner 130made of glass would break. Furthermore, if the inner diameter of the endportion 144 is greater than or equal to 100% of the outer diameter ofthe burner 130, the air-tight seal around the burner 130 at the endportion 144 cannot be ensured.

The burner boot 140 receives the radiant heat of the flame emitted fromthe burner 130, and is exposed to the hydrogen chloride generated fromthe reactions in the reaction chamber 110. Therefore, the material forforming the burner boot 140 may have thermal resistance of at least onehundred and tens of degrees and oxidation resistance to hydrogenchloride. By having a suitable flexibility, the stress placed on theburner can be further reduced as a result of the reaction chamber andthe like absorbing the thermal displacement.

More specifically, this material can be exemplified by silicon resin ormodified silicon resin. If the material used for the burner boot 140 issilicon resin, by setting the thickness of the connecting portion 143 tobe at least 0.2 mm and no greater than 3 mm, it is possible toeffectively prevent the transfer of stress between the ends of theburner boot 140. Furthermore, by forming the connection portion betweenthe burner boot 140 and the reaction chamber 110 to have a durometer Ahardness that is at least 30 and no greater than 60, it is possible toeffectively maintain the air-tight seal of the connection portion.

Upon manufacturing a porous glass base material to serve as the opticalfiber base material 210 using the manufacturing apparatus 10 describedabove, no leaking of the generated microparticles or the like to theoutside of the reaction chamber 110 was found during the manufacturing.Furthermore, a transparent glass base material was manufactured bysintering the porous glass base material manufactured using themanufacturing apparatus 10. No gas bubbles caused by impurities werefound in this transparent glass base material.

FIG. 4 is a graph showing the refractive index distribution in theradial direction measured at a certain position in the longitudinaldirection of an optical fiber base material 210 with a trunk length of1200 mm obtained in the manner described above. As shown in the drawing,the region near the center of the optical fiber base material 210 wasformed by SiO₂ doped with Ge, and therefore had a high refractive index.From the refractive index distribution shown in the drawing, it ispossible to calculate the relative refractive index difference Δ of theoptical fiber base material 210, as shown in the drawing.

Furthermore, upon measuring the relative refractive index difference Δat intervals of 20 mm along the longitudinal direction of the opticalfiber base material 210 described above, it was found that the averagevalue of the relative refractive index difference Δ was 0.368% and thestandard deviation was 0.003(%) across the entire trunk portion of theoptical fiber base material 210. In this way, it was found that thestandard deviation was small for the optical fiber base material 210manufactured using the manufacturing apparatus 10 of the embodimentdescribed above.

(Comparative Example)

FIG. 5 schematically shows the structure of another manufacturingapparatus 20 prepared as a comparison. The manufacturing apparatus 20has the same structure as the manufacturing apparatus 10 shown in FIG.1, aside from the points described below, and can be used to manufacturean optical fiber base material 210 using VAD. Components that are thesame as those shown in FIG. 1 are given the same reference numerals, andredundant descriptions are omitted.

The manufacturing apparatus 20 differs from the manufacturing apparatus10 shown in FIGS. 1 and 2 with regard to the shape of the seal member180 that forms the air-tight seal between the burner 130 and theprotruding portion 111 of the reaction chamber 110. Specifically,instead of the burner boot 140 of the manufacturing apparatus 10, themanufacturing apparatus 20 includes a seal member 180 shaped as a roundlid.

The seal member 180 is formed of silicon rubber in the same manner asthe flange portion 142 of the burner boot 140, and has a through-holeformed in the center thereof. The seal member 180 has an outer diameterof 80 mm, an inner diameter of 24 mm, and a thickness of 4 mm. The outercircumferential edge of the seal member 180 is clamped by a sealpressing jig 181, together with the flange portion 112 of the reactionchamber 110. As a result, the seal member 180 forms an air-tight sealwith the reaction chamber 110, thereby creating an air-tight spacebetween the reaction chamber 110 and the seal member 180.

The outer diameter of the burner 130 inserted into the seal member 180was 25 mm. As a result, the through-hole of the seal member 180 waswidened by the burner 130, and an air-tight seal was formed between theseal member 180 and the burner 130 as a result of the elasticity of theseal member 180. In this way, an air-tight seal was formed between thereaction chamber 110 and the burner 130.

Aside from using the manufacturing apparatus 20, a porous glass basematerial was manufactured under the same conditions as the manufacturedexample. During manufacturing, there was no leaking of generatedmicroparticles to the outside of the reaction chamber, but the angle ofelevation of the burner changed slightly due to thermal displacement ofthe reaction chamber. When this porous base material was heated tobecome transparent glass, the resulting transparent optical fiber basematerial 210 had the refractive index distribution shown in FIG. 6.

No gas bubbles caused by impurities were found in the resulting opticalfiber base material 210, but upon measuring the relative refractiveindex difference Δ in the same manner as shown in FIG. 4, it was foundthat the average value of the relative refractive index difference Δ was0.343% and the standard deviation was 0.010(%) in the longitudinaldirection of the optical fiber base material 210. It was thereforedetermined that the standard deviation is worse when using themanufacturing apparatus 20 according to the comparative example.

In this way, by using the manufacturing apparatus 10 according to theembodiment described above, leaking of the raw material gas to theoutside of the reaction chamber 110 is prevented and stress of thereaction chamber 110 caused by temperature change is prevented fromaffecting the burner 130. Therefore, fluctuation of the set position andangle of elevation of a preset burner is prevented, and themanufacturing conditions of the optical fiber base material arestabilized. Accordingly, it is possible to manufacture an optical fiberbase material that has a stable refractive index profile in thelongitudinal direction.

While an embodiment of the present invention has been described, thetechnical scope of the invention is not limited to the above describedembodiment. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiment. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

What is claimed is:
 1. An optical fiber base material manufacturingapparatus comprising: a reaction chamber; a burner that has a portionthereof inserted into the reaction chamber through an insertion openingthat creates a connection between the inside and outside of the reactionchamber, and emits a flame toward a starting member positioned withinthe reaction chamber; and a seal connection member that creates anair-tight seal between the burner and the reaction chamber at theinsertion opening, wherein one end of the seal connection member firmlycontacts the burner inserted therethrough, another end of the sealconnection member firmly contacts the reaction chamber and has athrough-hole formed therein through which the burner is inserted withoutcontacting the seal connection member, the seal connection memberincludes a connecting portion that connects the one end to the anotherend, while preventing transfer of stress between the one end and theanother end, and an inner diameter of the seal connection memberdecreases from the another end of the seal connection member to the oneend of the seal connection member.
 2. The optical fiber base materialmanufacturing apparatus according to claim 1, further comprising: araising mechanism that raises and rotates the starting member positionedwithin the reaction chamber.
 3. The optical fiber base materialmanufacturing apparatus according to claim 1, further comprising: anexhaust pipe that ejects fluid from the inside of the reaction chamberto the outside.
 4. The optical fiber base material manufacturingapparatus according to claim 1, wherein the seal connection memberincludes the connecting portion that has a curved cross-sectional shapein a cross section including a central axis of the burner.
 5. Theoptical fiber base material manufacturing apparatus according to claim1, wherein the reaction chamber includes, in the insertion opening, aprotruding portion that protrudes to the outside of the reaction chamberand connects the inside and the outside of the reaction chamber, and theseal connection member creates air-tight contact with a tip of theprotruding portion.
 6. The optical fiber base material manufacturingapparatus according to claim 5, wherein the reaction chamber includes aflange portion on a tip of the protruding portion that extends along asurface intersecting a protrusion direction of the protruding portion,and firmly contacts the seal connection member at the flange portion. 7.The optical fiber base material manufacturing apparatus according toclaim 6, wherein the seal connection member includes a flange portion atthe another end that extends radially outward, and firmly contacts theflange portion of the protruding portion at the flange portion to createan air-tight connection.
 8. The optical fiber base materialmanufacturing apparatus according to claim 1, wherein the inner diameteris less than the outer diameter of the burner at the one end, and theseal connection member firmly contacts the burner due to a returningforce of elastic deformation caused by insertion of the burner.
 9. Theoptical fiber base material manufacturing apparatus according to claim8, wherein thickness of the connecting portion is less than thickness ofthe seal connection member at least at one of the one end and theanother end, and when the at least one of the one end and the anotherend is deformed, deformation of the connecting portion prevents stressfrom being transferred between the one end and the another end.
 10. Theoptical fiber base material manufacturing apparatus according to claim1, wherein the seal connection member has thermal resistance to maintaina shape against a flame emitted by the burner, and has oxidationresistance to restrict oxidation due to raw material gas introduced intothe reaction chamber.
 11. The optical fiber base material manufacturingapparatus according to claim 1, wherein the seal connection memberincludes a portion formed of a flexible material.
 12. The optical fiberbase material manufacturing apparatus according to claim 11, wherein theflexible material includes resin.
 13. The optical fiber base materialmanufacturing apparatus according to claim 12, wherein the sealconnection member is formed of a material including at least one ofsilicon resin and modified silicon resin.
 14. The optical fiber basematerial manufacturing apparatus according to claim 13, wherein theinner diameter is greater than or equal to 80% and less than 100% of anouter diameter of the burner.
 15. The optical fiber base materialmanufacturing apparatus according to claim 13, wherein the connectingportion connecting the one end and the another end of the sealconnection member has a thickness that is greater than or equal to 0.2mm and less than or equal to 3 mm.
 16. The optical fiber base materialmanufacturing apparatus according to claim 15, wherein the connectingportion connecting the one end and the another end of the sealconnection member has a durometer A hardness that is greater than orequal to 30 and less than or equal to
 60. 17. The optical fiber basematerial manufacturing apparatus according to claim 1, wherein the sealconnection member is dome-shaped.